Many machines of the rotary abutment type have been proposed heretofore, and some such machines have been suggested for use as rotary engines, but in practice their use has been isolated to either pumps or liquid operated motors (for example oil motors).
Rotary abutment machines comprise many types, from simple gear pumps or motors to sliding vane pumps or motors and included amongst the types which have been proposed but which are not in general use, is a rotary machine which may be defined as follows:
A plurality of rotors rotatable within respective parallel intersecting bores in a stator, at least one of said rotors being a compression rotor and having an axially extending lobe radially outstanding therefrom, which upon rotation, sealably co-operates with the curved surface of its respective said bore,
ANOTHER SAID ROTOR BEING A GAS TRANSFER ROTOR AND HAVING A ROLLING SURFACE IN GAS SEALING CONTIGUITY WITH THE CURVED SURFACE OF ITS RESPECTIVE BORE AND CONTAINING AN AXIALLY EXTENDING GAS TRANSFER RECESS WHICH EXTENDS RADIALLY INWARD FROM ITS ROLLING SURFACE, AND
DRIVE MEANS COUPLING THE COMPRESSION ROTOR TO ROTATE IN ONE DIRECTION AND THE GAS TRANSFER ROTOR TO ROTATE IN THE OPPOSITE DIRECTION,
THE AXES OF THE ROTORS BEING ARRANGED SO THAT, UPON ROTATION, THE RECESS SURFACE IS ENTERED BY SAID LOBE, AND WHEN THE LOBE IS NOT WITHIN THE RECESS, THE ROLLING SURFACE OF THE COMPRESSION ROTOR LIES IN GAS SEALING CONTIGUITY WITH THE ROLLING SURFACE OF THE GAS TRANSFER ROTOR. Said machine was the subject of British Patent 560987 (Everleigh) which is discussed below.
There are theoretical advantages to be achieved over piston engines for example, but these advantages have heretofore not been fulfilled. One advantage is that a more effective use is made of the thrust from expanding gases against a lobe. In a piston engine, both the induction and compression strokes are short in relation to the complete cycle whereas with a rotary abutment type machine the strokes are relatively long. A higher degree of expansion can be attained with a long stroke rotary abutment type machine, thereby utilizing the characteristics of expanding gases. In some piston engines, the exhaust gases are not completely swept out of the working chamber. In all piston engines, special dynamic balancing methods are required to reduce vibration. The highest speed attainable from a piston engine under good working conditions is about 6,000 rpm, although higher speeds have been attained for special purposes. A piston engine is characterised by many rubbing and frictional surfaces required to seal the working chamber, and also by considerable windage of the working parts. Much power loss results from these disabilities. Since a piston engine has its piston moving at a relatively low speed when ignition takes place, an exhaust gas is produced which includes oxides of nitrogen, unburnt hydrocarbons, other undesirable polluting gases and particulates (oil smoke etc.).
In the British Patent No. 560987 issued to E. F. Everleigh there was proposed a rotary abutment type machine of the above defined type having two compression rotors, two power rotors and one gas transfer rotor, wherein the outermost rotors and the intermediate rotor were all of frusto conical shape, and provision was made for axial movement of the intermediate rotor. The outer surfaces of the chambers had ends which were of curved shape in cross-section, whereas the recess of the rotor extended for the full length of the rotor, thus providing excessive leakage paths. For this reason the engine could only be suitable for very high speed operation, as for example would be associated with gas flow speeds utilised in gas turbines. However the surfaces of the intermediate and outer rotors were urged into firm contact, there being a resultant rubbing speed between the surfaces which would impart undesirable loading to the machine and reduce possibility of such high speeds. The most important disabilities with the engine described in that Patent specification however, were firstly the difficulty in disposing of gases entrapped in the intermediate rotor recess by the lobes of other rotors (assuming that they could be modified and shaped to be workable), such gas essentially being ejected in contra-flow to the induced gases of the engine; and secondly, the poor cross-sectional shape of the recess which limits gas flow between the chambers.
In the British Patent No. 1,355,254 issued to J. Koltermann et al there was described a four rotor machine, there being three outer rotors and one intermediate rotor, and the machine being described as one useful for operating as an engine on compresed gas. The cross-sectional shape of lobe and recess was such as to entrap quantities of gas which again would be injected in contra-flow to the induction, and the recess does not otherwise perform a gas transfer function, axial ports being utilised.
In British Patent No. 1,177,593 issued to K. Lauer there was described and illustrated a three rotor machine wherein the V-section lobes co-operated with a circularly curved recess in an intermediate rotor, but it will be seen that contiguity between load tip and recess surface is lost during a critical portion of the rotation, and the device is limitied to hydraulic applications.
In British specification Nos. 604,972 and 610,068 both issued to Renolds Metals Company there was described an hydraulic machine utilizing two rotors, one having a lobe thereon, and the other having a recess, but contiguity of the lobe and recess surfaces again is lost during critical periods of rotation. A further British specification No. 725,823 issued to F. Berry illustrated a machine wherein there is absence of critical contiguity between the lobe and recess. These devices are not presented as suitable for used with compressible fluids.
Similarly said critical contiguity is lost in the British Patent No. 754,984 issued to Liquid Control Corporation, being a liquid transfer metering device for liquids, wherein there is no compression.
In the British Patent No. 784,554 there was described a rotary engine having lobes with involute surface co-operable with arcuate surfaces of recesses in an intermediate member, without any gas transfer function by the recess, again there being a loss of critical contiguity.
In order for a rotary abutment machine to have a reasonable output, (when used as a compressor or as an engine) it is necessary to maximise the lobe effective area. In practical engines much difficulty is encountered in achieving a design wherein a reasonably high compression ratio exists, wherein there is a smooth streamlined gas flow so that high rotational velocities can be achieved, and wherein there is a minimum of gas entrapped between lobe and recess. It should be noted that the problems encountered in an engine are much different from those encountered in hydraulic machines, some examples of which have been referred to above, because of gas compressibility. For example, we have found that a generated involute tooth form results in the entrapping of a relatively large volume of high pressure gas between the surfaces of the lobe and recess, and thereby also reducing the pressure which could be obtained if this volume was further reduced when this gas is released, it has a deleterious effect upon the induction of gases into the compressor portion of the machine. Under normal conditions the gas will be released towards the induction portion and will greatly reduce the free inward flow of gases into the induction space, of the compression cylinder.
Although the machine of this invention may be used as a compressor or as a vacuum pump, its normal use is that of a rotary engine, and the terminology used herein will assume such use. The necessary changes in structure for use as a compressor or vacuum pump will either be explained hereunder or will be obvious to those skilled in the art.